Magnesium alloys containing Mg2Si particles, as a promising cheap heat-resistant magnesium alloy for automobile engine applications, are attracting more and more attention of both material scientists and design engineers. Refinement of the Chinese script Mg2Si particle is a key for using this kind of alloy in sand casting or permanent mould casting. In the present work, a new type of heat-resistant magnesium alloy with low cost based on Mg-Al-Zn-Si is developed. The effect of Sb addition and mischmetal. (MM, a mixture of rare-earth, RE elements) microaddition on the microstructure, solidification process, mechanical properties and corrosion resistance of Mg-Al-Zn-Si alloy is investigated systematically. The result shows that Sb promotes the formation of fine polygonal-type Mg2Si particles by providing the nucleation sites. Meanwhile, the grain sizes of Sb modified Mg-Al-Zn-Si alloy are much finer than that of the base alloy. Such improved microstructure of the modified alloy results in significant improvement in tensile properties, toughness and creep resistance at elevated temperatures up to 200degreesC, which exceed or are comparable to AE42 alloy. Moreover, the corrosion resistance of the new alloy is improved greatly by MM microaddition.